Multi-mode temperature compensated filters and a method of constructing and compensating therefor
First Claim
1. A microwave filter comprising an input and output and a first cavity made of a material having a coefficient of thermal expansion and resonating at an operating frequency in at least two orthogonal modes substantially simultaneously, said cavity having a volume that is changeable with temperature, said cavity containing solid dielectric material having a dielectric constant that varies with temperature, said dielectric material being sized so that it does not resonate at the operating frequency of the cavity, there being at least one amount of said dielectric material having a value of a temperature coefficient of the dielectric constant to compensate for changes in the volume of the cavity with temperature to at least reduce a variation in said operating frequency that would otherwise by caused by a temperature-induced volume change of said cavity.
1 Assignment
0 Petitions
Accused Products
Abstract
Multi-mode waveguide filters are temperature compensated using dielectric material contained within at least one cavity of a filter. The variation in operating frequency of the filter that would otherwise result from changes in temperature is substantially balanced by a change in operating frequency with temperature caused by a change in a dielectric constant of the dielectric material so that the operating frequency of the filter remains substantially constant with temperature. The filter can have one or more dual-mode or triple-mode cavities. In a method of constructing and compensating a filter, the amount of dielectric material is selected so that the dielectric material does not resonate at the operating frequency of the cavity, the amount of dielectric material in the cavity being adjustable after each cavity is constructed. The cavity is operated with a fixed amount of dielectric material contained in the cavity for each mode and the change in operating frequency of the filter with temperature is determined. If the change in operating frequency of the filter is not at an acceptable level, the amount of dielectric material contained in the cavity for each mode is varied and the filter is operated through a range of temperatures to determine whether the change in operating frequency is then at an acceptable level. These steps are repeated until the change in operating frequency of the filter is at an acceptable level.
-
Citations
48 Claims
- 1. A microwave filter comprising an input and output and a first cavity made of a material having a coefficient of thermal expansion and resonating at an operating frequency in at least two orthogonal modes substantially simultaneously, said cavity having a volume that is changeable with temperature, said cavity containing solid dielectric material having a dielectric constant that varies with temperature, said dielectric material being sized so that it does not resonate at the operating frequency of the cavity, there being at least one amount of said dielectric material having a value of a temperature coefficient of the dielectric constant to compensate for changes in the volume of the cavity with temperature to at least reduce a variation in said operating frequency that would otherwise by caused by a temperature-induced volume change of said cavity.
- 33. A method of constructing and compensating a microwave filter having a first cavity resonating at an operating frequency in at least two orthogonal modes substantially simultaneously, said cavity being made of a material having a coefficient of thermal expansion and having a volume that changes with temperature, said method comprising the steps of selecting one amount and type of dielectric material to be contained within said cavity for each mode, selecting the amount of dielectric material so that the dielectric material does not resonate at the operating frequency of the cavity, selecting the dielectric material with a dielectric constant and a temperature coefficient for the dielectric constant to compensate for changes in the volume in the cavity with temperature to at least reduce a variation in said operating frequency that would otherwise be caused by a temperature-induced volume change of said cavity.
Specification